1. Field of the Invention
The present invention generally relates to a technique for detecting changes or differences in an object over a predetermined time period.
2. Description of the Prior Art
Various areas of technology require the ability to determine the changes that occur in an object over a predetermined period of time. For example, in certain surveillance systems, the existence of any change in a scene being monitored by, say, a television camera, may indicate the presence of an intruder. In video transmission systems, the ability to detect frame-to-frame changes has been used to eliminate redundant information corresponding to non-varying areas of the object, thus enabling transmission of only data indicative of significant variation. Also, in apparatus such as a bubble chamber used to display the trajectories of atomic particles, the ability to separate time variant information in the monitored object from the stationary background information greatly enhances the usefulness of such apparatus.
One presently known technique for comparing successive frames in a video system to detect temporal changes therein utilizes a frame memory to store information obtained by scanning the first frame. When the second frame is scanned, the information then derived is interleaved with the stored data, and a point-by-point comparison is made. This technique, however, has several disadvantages. First, the frame memory is costly, especially where good resolution requires a large amount of data. Second, data from the first and second frames must be carefully synchronized or registered, so that corresponding points of the object are properly aligned. Third, this technique, while adequate to detect certain changes, is not fast enough for use where comparisons over very short time intervals are necessary, since scanning of the first frame must be completed before the comparison can begin. Moreover, even if scanning is accomplished with separate cameras to reduce time delays, then the cost of the system is further increased, and the registration problem becomes still more difficult.
In view of the above difficulties, it is the broad object of the present invention to efficiently enable the direct comparison of successive images of a time variant object. Additional objects are the provision of such a system in which the differences in an object over a very short time period may be determined, in which a large capacity memory or other data storage apparatus is not required, and in which problems of image alignment or registration are obviated.